This invention relates generally to improvements in the laminated circuit boards used in electronic circuitry. Those boards which are used in relatively complicated pieces of equipment, such as main frame computers, must be of a high standard of quality in order to function in an efficient manner for a long period of time without failure. A lower standard of quality is adequate for consumer products such as personal computers, television equipment, radios, and the like.
Circuit boards usually comprise a multi-layer composite made of layers comprising a thermosetting polymer and a suitable reinforcing material. A major problem with multi-layer composites is the dimensional stability of the inner layers. When processing the composite, the inner layers are subjected to stress as the polymers thermoset and the temperature changes and the layers may expand or contract. This may cause registration problems, that is, the inner layers may not be interconnected at the intended places because they have moved during expansion or contraction. Failure to interconnect layers can be a cause for either failure or rejection of the composite.
Another area in which thermal expansion plays an important role is in carriers for silicon chips which are used in integrated circuitry. Silicon chips may be mounted on a chip carrier, such as ceramic or plastic which in turn is mounted on a chip carrier substrate or circuit board. In some instances, it is important that the electrical connection between the chip carrier and the chip carrier substrate is hermetically sealable and can withstand temperature cycling. When the package is subjected to temperature extremes, the solder joints may fracture causing an electrical open. In order to overcome this problem, the chip carrier or chip carrier substrate should have a rate of thermal expansion which assures that the soldered joints will not fracture during thermal cycling. Preferably, such materials should be dimensionally stable, that is, each layer of the laminates should expand or contract the same amount as the temperature changes.